The proposed research has one long-term goal: to elucidate the role of eicosanoids and their biosynthetic pathway in regulating neuronal activity. Studies outlined in this proposal will test the specific hypothesis that endogenously synthesized eicosanoids regulate ionic currents determining spontaneous action potential amplitude durations and frequencies in snail pacemaker neurons. Parallel experiments will be done using sensitive assay methods for measuring eicosanoid release and standard electrophysiological techniques for intracellular voltage and voltage clamp recordings. Experimental objectives are: 1) to determine the profile of endogenously synthesized eicosanoids in subesophageal ganglia of the snail, Helix aspersa; 2) to study extracellular eicosanoid concentrations and spontaneous action potentials as affected by single eicosanoid end-products, inhibitors of eicosanoid synthesis and precursor essential fatty acids; 3) to identify ionic currents most affected by changes in extracellular eicosanoid concentrations; and 4) to see whether time-dependent changes in eicosanoid synthesis are correlated with changes in action potentials and ionic currents under control and experimental conditions. The proposed studies are an unique interface between eicosanoid research and neurophysiology; as such, they are expected to be extremely productive. They will provide information for developing a comprehensive understanding about the relationship between eicosanoids and ion fluxes which is currently under intense investigation using biochemical and pharmacological techniques. They should help to clarify the ionic mechanisms affected by indomethacin, a common therapeutic agent, thereby providing information which might be used for developing more specific anti-inflammatory drugs with lower toxicity. Results of these studies may also have broad biological significance. Molluscan pacemaker neurons are used as models for studying the ionic mechanisms underlying pacemaker activity in mammalian cells which are less accessible for experimental study. Based on preliminary studies, the synthesis of at least PGE2 appears to regulate ionic currents generating pacemaker potentials in the snail A-cell.